1. Field of the Invention
The present invention relates to a method for measuring a reference point of an inclined rotating table at the time of machining using the inclined rotating table by a wire electric discharge machine and a measuring jig used for the measurement.
2. Description of the Related Art
In recent years, machining using an inclined rotating table has often been performed in wire electric discharge machines. For example, machining a gear having an inclined surface, such as a bevel gear, using a wire electric discharge machine has often been performed in these years. Since a wire electrode can be ordinarily inclined only by up to about 45° in machining (taper machining) of an inclined surface using a wire electric discharge machine, a bevel gear having a cone angle of, for example, 60° cannot be machined. It is thus common to attach a piece of work to a rotating table, incline the rotating table to near a cone angle of a bevel gear, and machine the piece of work with a wire electrode nearly vertical, when the piece of work is to be made into the bevel gear.
In general machining using a rotating table, a program is created using a point of intersection of a table center of the rotating table and a work-fixed surface as a reference point. In order to cause the reference point defined at the time of the program creation coincide with a coordinate position on an actual machine, the coordinates of the reference point on the machine need to be measured.
If a table center of a rotating table is parallel to an X-Y plane, reference coordinates on a machine are generally obtained by adjusting a jig in the shape of a round bar, called a test bar, such that the table center of the rotating table and a table center of the test bar coincide with each other, fixing the test bar to a work-fixed surface of the rotating table, and measuring the position of the test bar using a wire electrode or a probe.
In the case of machining with an inclined rotating table, reference coordinates can be measured using a probe with a test bar as described earlier fixed in the same manner. In a measuring method using a wire electrode, however, an end face edge of a test bar needs to be a sharp edge. In practice, a measurement error occurs due to the difficulty of machining of a sharp edge and the difficulty of stable measurement of an edge.
Additionally, a wire electrode center is separate from a probe center in a general wire electric discharge machine, and a relative distance between the centers is difficult to accurately obtain. Even if a relative distance is accurately obtained, the relative distance needs to be obtained with each probe replacement. This increases the time for measurement work.
Although a technique for measuring a machining reference point on an inclined rotating table is disclosed in Japanese Patent Laid-Open No. 2010-274337, the technique does not use a contact sensing function of a wire electrode which a wire electric discharge machine generally has.